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DISPLAYING POSTS TAGGED: geology (4)

Lisa works in the Public Programs Department at Melbourne Museum but also volunteers in the Palaeontology Department and has been on several fossil digs.

By the tenth day of the annual Dinosaur Dreaming dig we had already catalogued more than 140 fossils. To know where to dig in the first place we need to understand the geology of the area because the types of rock and how they have been laid down can give us much information about the palaeoenvironment. Dr Alan Tait, Adjunct Research Fellow in the Department of Geosciences at Monash University is currently researching the sedimentology of the Flatrocks site and kindly explained its geology to me.

Today the site known as Flatrocks is a rocky beach dominated by light grey sandstone but 120 million years ago during the Cretaceous, the environment was very different. Australia was once part of a supercontinent called Gondwana which also comprised Antarctica, South America, Africa, New Zealand and India.

Much of Gondwana had broken up by the Cretaceous and a rift had started to form between Australia and Antarctic. The types of rocks and fossils we find along the coastline in Inverloch today tell us the story of the rift valley and the animals and plants that lived there.

The cliff face near the Flatrocks site. The grey mudstone is the remains of a flood plain which was on the floor of the rift valley. The layer where we find most of our fossils lies above this and at the top is massive sandstone. To the left of the mudstone you can see a fault where the rock layers have shifted dramatically from their original horizontal deposition.Image: Lisa NinkSource: Museum Victoria

The fossil layer itself consists of the sedimentary rocks, grey sandstone and conglomerate that were deposited during flooding of the rift valley. The conglomerate pebbles are made of clay eroded from the flood plain soils during flooding. The sandstone is grey because it contains grains of volcanic rock eroded from active volcanos some distance away and washed into the rift valley. The sediments also include the fossilised remains of dead animals, plants and trees. The time between the floods was long enough for large trees to grow, perhaps at least 100 years, and the floods were catastrophic.

“The main fossil bearing layer (under the red line) consists of grey sandstone with coal throughout it. The layer is bounded by a layer of mudstone below and massive sandstone above.Image: Lisa NinkSource: Museum Victoria

There are many fossilised tree stumps on the shore platform. Some of these trees lie horizontally with their fossilised roots still attached and are believed to have been knocked over by the force of the floods and washed down the river. We also find fossil leaves of ferns, gingkoes and monkey puzzle-like trees that once grew as part of a forest within the rift valley.

A fossil tree trunk. If you look closely you can even see the growth rings.Image: Lisa NinkSource: Museum Victoria

The coal in the fossil layer is the remains of decomposing plants that once grew in the valley. Fossilised grains of pollen from these plants have also been found and by identifying their species, we can date the sediments surrounding them.

A nearby dyke (a long straight crack in the rocks through which magma from deep below the Earth's crust travels upwards and cools) is made up of basaltic rock, another igneous rock type. The dyke is 99.5 million years old and cuts through the grey sandstone, meaning it formed after the sedimentary rocks had been deposited.

Ursula Smith works in the natural sciences collections at Museum Victoria. Though a palaeontologist by training she finds all the collections fascinating and swings between excitement at all the cool stuff in them and despair at the lack of time to look at it all.

I’ve been asking the people who work with MV collections what some of their favourite items are, starting with Dermot Henry, the Manager of the Natural Sciences Collections.

Dermot's speciality is geology and he’s looked after the geosciences collections for many years. When asked what his favourite item was he took care to tell me that he didn’t have a favourite because there are so many fascinating objects, but when pressed he picked the Murchison meteorite as "probably the most famous and scientifically important rock in the collections."

The Murchison meteorite is one of 16 meteorites known from Victoria, and is rare in that it was actually observed falling, rather than just being found on the ground, so it came to scientists fresh (other than some surface dirt from falling into mud and cowpats and the like). It exploded in the atmosphere over Murchison, Victoria, about 160km north of Melbourne, on 28 September, 1969 and fell over an area around 35km2. So when we talk about 'it' we’re really talking about lots of broken pieces of a single object.

Display in Dynamic Earth.Image: Ursula SmithSource: Museum Victoria

These pieces are on display in Dynamic Earth and are just a very small portion of what was collected. The largest piece found weighed nearly 7kg though many more were just a few grams each. In total, around 100kg was collected and over 80kg of that made it into science collections. While a lot of the material went overseas (mostly to the Field Museum in Chicago who have nearly 52kg and the Smithsonian in Washington DC who have nearly 20kg) some remained in Australia. Over 7kg stayed at the University of Melbourne and much of this was later donated to Museum Victoria. We have about 3.5kg and only the largest pieces that are on display; we also have lots of smaller pieces.

Most of the pieces of rock in this drawer are parts of the Murchison meteorite (though not the big rock on the right – that’s actually a different meteorite of a similar type called Rainbow that was found in Victoria in 1994). Opening the sealed tubes, you can still smell, very faintly, what Dr. John Lovering from the University of Melbourne who organised the collection of the meteorite pieces in 1969 described as "just like methylated spirits – very strong". This was the first indication that the meteorite he was looking at was a rare type called a carbonaceous chondrite. Unlike more common rocky meteorites, a carbonaceous chondrite is packed full of organic molecules and a lot of water; this one is eight per cent water.

The year after it was collected, papers began to appear in scientific journals describing the chemical composition of the meteorite and excitement about its scientific significance began to grow. A paper in the journal Nature describing the discovery of amino acids of extra-terrestrial origin in the meteorite made, if you’ll pardon the pun, quite an impact, and was widely covered in the press, even making it into Time Magazine. Papers are still being published on it – one came out in August this year in the Proceedings of the National Academy of Sciences, and a new chromium sulfide mineral, Murchisite (Cr5S6), was just reported in American Mineralogist.

To date over 70 amino acids have been identified from the meteorite, only 19 of which are known from Earth. These, and the many other chemicals that have been identified, suggest there could be thousands of complex organic chemicals present. What’s so interesting about these molecules is that they demonstrate that the simple chemical building blocks necessary for life on Earth seem to form quite easily in other places.

It isn’t just the origins of life that the Murchison meteorite may tell us about. It contains tiny pre-solar grains – nano-diamonds and silicon carbides, among others, that formed in supernovas long before our own sun appeared – which tell us a lot about how our own, and other, solar systems formed. But not only that, information from the pre-solar grains in the Murchison meteorite has been fundamental in figuring out a lot about how elements are originally produced and a lot about the structure and mechanics of stars.

So the Murchison meteorite is definitely pretty cool – biologists, chemists, astrophysicists and those of us who just think rocks that fall out of the sky are fascinating all agree on that. As Dermot says, "it’s so unusual and it’s yielded so much information about cosmology, element formation and how the universe works – it’s probably generated more publications than any other meteorite. And it’s Victorian!"

Two pieces of the Murchison meteorite in Dynamic Earth.Image: Ursula SmithSource: Museum Victoria

When Natural Sciences Collection Manager Dermot Henry heard a radio report about efforts to salvage gold from the Royal Charter shipwreck, the story rang a bell. "I had recollections of seeing a little gold specimen that had come from a shipwreck." Sure enough, in the Geology Collection he located a small nugget with a curious label explaining that it was a survivor of the Royal Charter, which was lost off the coast of Wales in 1859. The typed label probably accompanied the nugget on display at the former Industry and Technology Museum. It reads in part:

One of the passengers had a part of his property in a belt round his waist, and in swimming ashore was dashed against the rocks and the belt burst where this was picked up but his life was saved after being three times washed back into the sea off the rock. Name of above passenger W. J. Ferris.

The ship was just three hours from its destination in Liverpool when a terrible storm drove it onto rocks. Carrying over four hundred people and gold worth millions in today's money, the loss was a terrible one for Australia and England. Many of the passengers were returning home after striking it rich in the central Victorian goldfields. Just a handful of people survived including the man on the label – William J. Ferris, a Ballarat shopkeeper.

The gold nugget that survived the Royal Charter shipwreck. It is 17mm long and weighs about 4g.Source: Museum Victoria

Dermot tracked the specimen back to a donation to the Public Library, Melbourne, from Mr Gordon Thomson, reported in the Argus in 1874. "We don't know how Thompson ended up with the gold," says Dermot. The report says that the two men met in Ireland but the nature of their transaction is not recorded.

Thomson himself was quite a character with a habit of collecting curious things. Irish-born into a wealthy family, he spent much of his life travelling the world and amassing ethnographic objects. His "very fine mansion" in Belfast called 'Bedeque-house' held "rich stores of curiosities and relics gathered from many lands." Among the relics were at least two treasures from Victorian history from his first visit to Melbourne in 1835, when the city was in its wattle-and-daub infancy. There he befriended William Buckley, who absconded from imprisonment to live with the Aboriginal people of Port Phillip Bay for more than 20 years. Buckley gave Thomson a greenstone axe-head that had "passed 20 years of its life of usefulness in Buckley's belt." The axe head and the Royal Charter gold specimen ended up in the Belfast museum along with hundreds of other objects Thomson collected on his travels.

When Thomson decided to return to Melbourne to live, he requested that the Belfast museum return the colonial objects, believing that they rightly belonged in their home country. Thus, in 1874, they travelled back over the oceans and were deposited in Melbourne public collections. We still have the gold but Buckley's axe has been missing for many years, its whereabouts unknown. Thomson built another 'Bedeque-house' in Dudley Street, West Melbourne. His 1886 obituary mourned the "death of one of the oldest Melbourne residents."

Following Dr Mark Norman's Warrnambool pub chat about chemistry and communication in deep sea animals on 2 August, the second Backyard Science at the Pub rolls into Bendigo tonight.

Geologist Dermot Henry will explore the origins of crystals and minerals found in central Victoria. The geological processes that made central Victoria such a booming gold-mining area also produced all kinds of other fascinating minerals; studying these helps us understand the rich chemistry of the Earth.

Dermot has worked at Museum Victoria since 1982 and has managed Museum Victoria’s Natural Science collections since 2001. He was responsible for the development of geological themes and content and the selection of specimens for the Dynamic Earthexhibition at Melbourne Museum.

Backyard Science at the Pub is part of National Science Week 2011 and will be held Tuesday 16 August 6pm – 8pm at The Foundry Hotel, 366 High Street, Bendigo. For enquiries or to register your interest, please email or telephone 0412 607 525.